Electret Microphone

Electret Microphone

A graphic illustrating an electret microphone. The circuit and prototype board symbols and a simple diagram of its connections are shown and labelled.

An electret microphone is a type of electrostatic capacitor-based microphone, which eliminates the need for a polarizing power supply by using a permanently charged material.

An electret is a stable dielectric material with a permanently embedded static electric charge (which, due to the high resistance and chemical stability of the material, will not decay for hundreds of years). The name comes from electrostatic and magnet; drawing analogy to the formation of a magnet by alignment of magnetic domains in a piece of iron. Electrets are commonly made by first melting a suitable dielectric material such as a plastic or wax that contains polar molecules, and then allowing it to re-solidify in a powerful electrostatic field. The polar molecules of the dielectric align themselves to the direction of the electrostatic field, producing a permanent electrostatic "bias". Modern electret microphones use PTFE Polytetrafluoroethylene plastic, either in film or solute form, to form the electret.

An electret microphone is a device that uses two conducting plates to capture sound waves and translate them into electrical waves. This simple design is found in other types of capacitor microphones, except here less power is needed thanks to a conducting plate with an attached insulator.

An electret microphone is an omnidirectional microphone, which means it can capture sound from all directions. It is one of the most widely used types of microphones in any field where a microphone is needed. Its good performance and inexpensive quality makes it very popular all around the world for different uses. What sets it apart from types of microphones is how it transmits sounds to output devices.

The Design of Electret Microphones:

It uses two conducting plates; one is fixed while the other is a vibrating diaphragm. This kind of design is found in all capacitor microphones, which are types of microphones that deliver great sound quality but requires a constant source of electrical charge to produce electrical signals that communicates the sounds made by the diaphragm into sound that comes out of outputs devices likes speakers. What makes it different from generic capacitor microphones is that it does not need a constant source of electrical charge. Its diaphragm is actually made of insulating material that contains a permanent electrical charge. This makes it very efficient by producing quality sounds without requiring a constant source of electrical charge.

This kind of design usually makes the diaphragms heavier because of the insulating material, but newer electret microphone designs feature a more efficient design wherein the insulating material is attached to the stationary back plate and not to the diaphragm, making it lighter and thinner, providing a more energy efficient microphone that produces roughly the same sound quality as capacitor microphones.

How Electret Microphones Work:

With the diaphragm and the back plate ready to receive sound waves, they work by letting the incoming sound waves from a source of sound from any direction to change the capacitance between the two conducting plates. The diaphragm is the conducting plate that receives the sound waves and it causes the change in capacitance. This change in capacitance produces variance in voltage on the back plate and this, in turn, sends electrical signals to output devices like speakers and sound systems. It may seem magical and mind-blowing, but this technology has been around for decades. Its simplicity lets it stand the test of time and even with some modifications through the years, the basic principle of using two conducting plates to deliver electrical signals that represent sound waves is still there.

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